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  1. #1
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    What is Preload?

    Hello everyone,

    I have a 2010 TREK 4500 with a Suntour SF10-XCM-PM-HLO w/coil spring and I was wondering what is preload and what is it for?

    I just got into mountain biking some I'm REAL ignorant!

    Thank you.

  2. #2
    coprolite fietsbob's Avatar
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    'preload' applies to bearing adjustments, such as your Headset ..
    your fork steering bearings.

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    Suspension preload puts compression on the spring.

    The more you dial up the suspension preload, the more force it will take to start to compress the suspension. It will also be stiffer throughout the suspension's travel.

    High preload makes pedaling more efficient because you waste a lot of energy when each pedal stroke makes the bike bob up and down.

  4. #4
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by fietsbob View Post
    'preload' applies to bearing adjustments, such as your Headset ..
    your fork steering bearings.
    Wrong preload. garage sale has it about right. The only thing to add is that with a high preload, the suspension is going to be harsher.
    Stuart Black
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  5. #5
    bike whisperer Kimmo's Avatar
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    Yeah, not much fun it it's smacking into the end of its travel all the time, I bet.

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    The preload adjustment on your fork is to adjust "sag" or how much the fork compresses under the static weight of you and your bike. This is to reduce "topping out", as Kimmo notes. Your fork manual should have a recommended sag setting but, in general, it's around 15-25 percent of your fork's total suspension travel, e.g. 15-25mm on a 100mm fork.

    To adjust, wrap a zip tie around one fork leg and, with all weight off of the fork, push the tie down the leg against the fully extended fork lower. Then, sit astride your bike in a normal riding position. Your and the bike's weight on the fork will cause it to compress somewhat and move the zip tie up the fork leg. Get off the bike and measure how far the tie moved up from its unweighted position. That's sag. Turn the preload adjustment knob to increase or decrease sag to match Suntour's recommended settings. Good luck!

  7. #7
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by pexio View Post
    The preload adjustment on your fork is to adjust "sag" or how much the fork compresses under the static weight of you and your bike. This is to reduce "topping out", as Kimmo notes. Your fork manual should have a recommended sag setting but, in general, it's around 15-25 percent of your fork's total suspension travel, e.g. 15-25mm on a 100mm fork.

    To adjust, wrap a zip tie around one fork leg and, with all weight off of the fork, push the tie down the leg against the fully extended fork lower. Then, sit astride your bike in a normal riding position. Your and the bike's weight on the fork will cause it to compress somewhat and move the zip tie up the fork leg. Get off the bike and measure how far the tie moved up from its unweighted position. That's sag. Turn the preload adjustment knob to increase or decrease sag to match Suntour's recommended settings. Good luck!
    I think Kimmo was referring to the other end of travel, or 'bottoming' out. Topping out is when the shock extends off of a drop and smacks the top of the fork.

    Sag isn't nearly as important in a spring fork as it is in an air fork. The spring can only hold up so much weight. You can't change it without changing the spring. With an air sprung fork, you can add or subtract air as needed to adjust the sag and ride quality.
    Stuart Black
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  8. #8
    Senior Member BCRider's Avatar
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    A GOOD spring fork will have adjustments for spring preload. In this case it appears that this is a fairly good quality fork since it has preload adjustment as well as a lockout for climbing.

    http://www.srsuntour-cycling.com/ind...nid=2605&sid=1

    Note that there's a link to an owner's manual at the bottom of the page which you can download.

    Pexio gave you some great info on how to set the sag. I'll just add in a hint that it helps if you have a buddy to move the zip tie. Get yourself onto the bike and into the position you'd be in during trail riding where you're actually going over obstacles. For most of us that means up on the pedals, arms and knees bent and back angled forward and fairly flat with head up. You'll want to be leaning against a wall or post lightly to do this. Bounce the bike lightly a couple of times to settle the suspension and THEN have your buddy run the zip tie to the seal. Then move your weight back and off the forks and dismount. The gap you have will be a more representative indicator of your static sag for how you ride when it's important to get the most out of your suspension.

    Then adjust your preload adjuster to set up this sag correctly. Obviously it needs to be measured again after each adjustment.

    If you're particulrly heavy or light then you may find that the springs are either too soft or hard to be able to reach the right preload adjustment. If you're really close to what it should be you can either live with it or get into the fork leg and add a small bit of additional packing or maybe trim down the preload adjuster size a little. If you're way off then you may need to find a different set of springs to make your fork work better with your weight.

    By the way, it's called "preload" because the springs are compressed or "preloaded" as they are fitted into the fork legs. If you ever have to open up for forks to do any work on them the first thing you must do is adjust out to the softest setting on the preload adjuster. Even then as you take your sprung leg(s) apart be sure to be pushing on the threaded cap so the cap doesn't spring out at you.
    Last edited by BCRider; 05-26-11 at 11:58 AM.
    Model airplanes are cool too!.....

  9. #9
    Don from Austin Texas
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    Quote Originally Posted by cyccommute View Post
    Wrong preload. garage sale has it about right. The only thing to add is that with a high preload, the suspension is going to be harsher.
    The term "preload" does indeed pertain to bearing adjustments as well as suspension.

    Don in Austin

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    Quote Originally Posted by Don in Austin View Post
    The term "preload" does indeed pertain to bearing adjustments as well as suspension.

    Don in Austin
    Also headset adjustments.

  11. #11
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Don in Austin View Post
    The term "preload" does indeed pertain to bearing adjustments as well as suspension.

    Don in Austin
    Thus the 'wrong' before preload. I didn't say that fietsbob was wrong about bearing preload but he was referring to something different from suspension preload which wasn't germane to ejoe's question.
    Stuart Black
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  12. #12
    Senior Member justadude's Avatar
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    Preload is the amount of blood delivered to the heart during diastole, or between its contractions.

  13. #13
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    I'll check the sag tomorrow and adjust as needed.

    And a Thank you to everyone who replied!

    I'll get back with how I did it and the results

  14. #14
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    ejoe, If the spring's preload adjust has to be turned in too many turns to adjust sag (your sitting on the bike should compress the fork a specific amount, instructions are brand specific) you'll need a stiffer spring. As you compress the spring you are closing the gap between each round of the coil, which reduces the range of travel available. This is more important if you have a multi rate spring than with a single rate spring.

    Brad

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